1. Field of the Invention
The present invention relates generally to the field of plasma physics. More particularly, the invention concerns a method and apparatus for compressing plasma to a high energy state.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
By way of brief background, in 1942, Enrico Fermi began discussing the idea of joining light nuclei by nuclear fusion to generate a large source of energy. He suggested burning deuterium, an abundant stable-isotope of hydrogen.
Today, the two primary approaches to the problem of achieving fusion power production have been Magnetic Confinement (MCF) and Laser Inertial Confinement (ICF) demonstration devices, such as the International Thermonuclear Experimental Reactor (ITER) tokamak that uses MCF or the National Ignition Facility (NIF) that uses ICF. These plasma experiments scale to very large sizes, measuring double-digit meters across.
Reactors based on these approaches scale to even larger sizes because they occupy either extreme of the density conditions necessary to fulfill the Lawson criterion for simultaneously achieving an energetic plasma for sufficient duration. MCF attempts to sustain a low-density 1020 m−3 plasma for a long duration of about 2 to 4 seconds, using external magnetic fields, but suffers from plasma instabilities. ICF attempts to hold a high-density 1028 m−3 plasma for nanoseconds. Magnetized Target Fusion (MTF) mitigates the problems encountered at either extreme by sustaining a medium-density 1024 m−3 plasma for only several milliseconds, while simultaneously reducing the minimum reactor size and cost as compared to MCF or ICF.
Los Alamos National Laboratory (LANL) began early research into MTF, but became hampered by the impetus to scale their experiments to use the nearby Shiva Star capacitor bank as a power source, instead of scaling by best available theory and experiment. The Shiva Star facility is located at Kirtland Air Force Base in Albuquerque, N. Mex. They did not optimize their proof-of-principle design based on physics, but rather on their power supply limitations. Another weakness in their approach was the use of a theta pinch, instead of a more efficient antenna method to form a Compact Torus (CT) plasma structure. Lastly, they adhere to a non-reusable compression method (an aluminum can crusher), for single-shot experimentation.
A Canadian company improved upon this earlier implementation and attempted a smaller-scale MTF approach, one with lower input energy needs. However, this approach introduced high-atomic-number impurities (such as lead) that quench the plasma by radiation losses before ignition occurs. Controlling the timing of the acoustic-compression method of this company is also problematic.
The California Institute of Technology and Lawrence Livermore National Laboratory (LLNL) focused on injecting a compact torus (CT) into a tokamak, to sustain the latter. Their prototype ‘Compact Torus Accelerator’ experiment showed that it was possible to both translate and compress a compact torus plasma structure by moving it relative to a tapered wall. However, they also experienced impurity problems (iron from steel electrodes) and did not attempt to extend their initial achievement to a curved geometry, such as a spiral.
The University of Washington Plasma Physics Laboratory has long advocated cleanliness requirements to avoid plasma impurities. They also utilize newer and more efficient methods to form and accelerate compact toroids. However, the pure research of the University is not focused on advanced plasma compression for MTF and the University has not attempted to translate a CT along a curved wall made of beryllium or lithium-silicon, which are much lower-Z materials than their walls (made of silicon dioxide).
Prior art compact toroid compression mechanisms, include, but are not limited to the following:    a. Explosive (liner technology)—For example the Los Alamos/Shiva Star and like projects. Such mechanisms are not reusable, require high input energy requirements and necessitate large system size.    b. Pneumatic (gas injection)—Such mechanisms typically exhibit pressure instabilities and are generally too slow for large plasmas.    c. Hydraulic (hydro-forming wall)—For example, the Canadian ‘General Fusion’ MTF concept. Such mechanisms, which require sub-microsecond-precision timing, require highly complex control systems. Also, the liquid walls of such mechanisms add high-atomic-number contaminants to the plasma that significantly increase radiation loss rates from the plasma.    d. Mechanical (piston)—For example, the Canadian ‘General Fusion’ concept. Such mechanisms, which require repetitive sub-microsecond timing, require highly complex control systems.    e. Electrical (relay-piston)—For example, the Canadian ‘General Fusion’ concept. Such mechanisms, which require repetitive sub-microsecond timing require highly complex control systems.    f. Magnetic (coil-current spike)—This mechanism has been tried in connection with many research programs, from the early TRISOPS (experiment at the University of Florida) to the University of Washington Plasma Physics Laboratory's latest CT devices. Such mechanisms require good timing, a large energy input, and may induce a plasma instability.